Various central nervous system disorders such as anxiety, depression, motor disorders, etc., are believed to involve a disturbance of the neurotransmitter 5-hydroxytryptamine (5-HT) or serotonin. Serotonin is localized in the central and peripheral nervous systems and is known to affect many types of conditions including psychiatric disorders, motor activity, feeding behavior, sexual activity, and neuroendocrine regulation among others. The effects of serotonin are regulated by the various 5-HT receptor subtypes. Known 5-HT receptors include the 5-HT1 family (e.g. 5-HT1A), the 5-HT2 family (e.g. 5-HT2A), 5-HT3, 5-HT4, 5-HT5, 5-HT6 and 5-HT7 subtypes.
The recently identified human 5-hydroxytryptamine-6 (5-HT6) receptor subtype has been cloned, and the extensive distribution of its mRNA has been reported. Highest levels of 5-HT6 receptor mRNA have been observed in the olfactory tubercle, the striatum, nucleus accumbens, dentate gyrus and CA1, CA2 and CA3 regions of the hippocampus. Lower levels of 5-HT6 receptor mRNA are seen in the granular layer of the cerebellum, several diencephalic nuclei, amygdala and in the cortex. Northern blots have revealed that 5-HT6 receptor mRNA appears to be exclusively present in the brain, with little evidence for its presence in peripheral tissues. The high affinity of a number of antipsychotic agents for the 5-HT6 receptor, in addition to its mRNA localization in striatum, olfactory tubercle and nucleus accumbens suggests that some of the clinical actions of these compounds may be mediated through this receptor. Therefore, 5-HT6 receptor ligands are believed to be of potential use in the treatment of certain CNS disorders such as anxiety, depression, epilepsy, obsessive compulsive disorders, attention deficit disorder, migraine, cognitive memory enhancement (e.g. for the treatment of Alzheimer""s disease), sleep disorders, feeding disorders (e.g. anorexia and bulimia), panic attacks, withdrawal from drug abuse (e.g. cocaine, ethanol, nicotine and benzodiazepines), schizophrenia, or the like; or in the treatment of certain gastrointestinal disorders such as irritable bowel syndrome.
Therefore, it is an object of this invention to provide compounds which are useful as therapeutic agents in the treatment of a variety of central nervous system disorders related to or affected by the 5-HT6 receptor.
It is another object of this invention to provide therapeutic methods and pharmaceutical compositions useful for the treatment of central nervous system disorders related to or affected by the 5-HT6 receptor.
It is a feature of this invention that the compounds provided may also be used to further study and elucidate the 5-HT6 receptor.
These and other objects and features of the invention will become more apparent by the detailed description set forth hereinbelow.
The present invention provides a chroman or benzofuran compound of formula I 
wherein
R is a C1-C6alkyl, aryl or heteroaryl group each optionally substituted;
R1 is halogen, CN, OR7, CO2R8, CONR9R10, SOxR11 or a C1-C6alkyl, C2-C6alkenyl, C2-C6alkynyl, C3-C6cycloalkyl, cycloheteroalkyl, phenyl or heteroaryl group each optionally substituted;
R2, R3 and R4 are each independently H or an optionally substituted C1-C6 alkyl group with the proviso that when R is an optionally substituted C1-C6alkyl group then R2, R3 and R4 must be H;
R5 and R6 are each independently H or a C1-C6alkyl, C3-C6cycloalkyl or heterocyclylalkyl group each optionally substituted or R3 and R4 may be taken together with the atom to which they are attached to represent a 3- to 10-membered optionally substituted mono- or bicyclic ring system optionally containing one or two additional heteroatoms selected from N, O or S with the proviso that when R is an optionally substituted C1-C6alkyl group then R5 and R6 must be other than a C3-C6cycloalkyl or cycloheteroalkyl group;
m is an integer of 1, 2, 3 or 4;
n is 0 or 1;
p is 0 or an integer of 1, 2 or 3;
 represents a single bond or a double bond;
x is 0 or an integer of 1 or 2;
R7 is H, CO2R12 or a C1-C6alkyl, C2-C6alkenyl, C2-C6alkynyl, aryl or heteroaryl group each optionally substituted;
R8 and R12 are each independently H or a C1-C6alkyl, C2-C6alkenyl, C2-C6alkynyl, C3-C6cycloalkyl, cycloheteroalkyl, aryl or heteroaryl group each optionally substituted;
R9 and R10 are each independently H or an optionally substituted C1-C6alkyl group; and
R11 is a C1-C6alkyl, aryl or heteroaryl group each optionally substituted; or
the stereoisomers thereof or a pharmaceutically acceptable salt thereof.
The present invention also provides methods and compositions useful for the therapeutic treatment of central nervous system disorders related to or affected by the 5-HT6 receptor.